新疆可支塔格—耸石山蛇绿构造混杂岩地球化学特征及意义  

Geochemical characteristics of the Kezhitage-Songshishan ophiolitic tectonic mélange in Xinjiang,China and their implications

作　　者：杨永锋 程犬 姜亚国 王新录 张文峰 朱国栋 唐静 YANG Yong-feng;CHENG Quan;JIANG Ya-guo;WANG Xin-lu;ZHANG Wen-feng;ZHU Guo-dong;TANG Jing(Shaanxi Mining Technology Industry Co.,Ltd.,Xi'an 710000,China;Regional Geological Survey Institute of Shaanxi Geology and Mining Group Co.,Ltd.,Xianyang 712000,China)

机构地区：[1]陕西地矿科技产业股份有限公司,陕西西安710000 [2]陕西地矿区研院有限公司,陕西咸阳712000

出　　处：《矿物学报》2022年第6期759-774,共16页Acta Mineralogica Sinica

基　　金：中国地质调查局地质调查项目(DD20160060)。

摘　　要：新疆且末县银石山地区可支塔格—耸石山蛇绿构造混杂岩是木孜塔格蛇绿岩带的西延部分,总体表现为强烈构造混杂的特征,主要包含蛇绿岩残片、上覆岩系、外来岩块及基质等部分。其中蛇纹岩与变橄榄岩等超基性杂岩中SiO_(2)含量为39.40%~41.51%、高MgO(37.97%~38.70%)、低TiO_(2)(0.01%)、低Al_(2)O_(3)(0.08%~0.72%)、低K_(2)O(0.02%~0.03%),Mg^(#)为84.36~84.90、m/f为10.70~11.09,属镁质超基性岩。稀土总量∑REE(4.70×10^(-6)~6.09×10^(-6))略高于球粒陨石的总量,(La/Yb)_(N)为5.80~7.72、δEu为0.84~1.13,轻稀土相对富集。Cr、Ni、Co元素含量较高,其中Ni元素已达边界品位,P、Nb、Zr、Hf等元素富集。岩浆岩中闪长岩类SiO_(2)、K_(2)O含量较低,MgO、CaO、Na_(2)O含量较高,在Al_(2)O_(3)-CaO-MgO图解中落入镁铁质堆晶岩区域,表明其也可能是蛇绿岩的组成部分。闪长岩类LREE/HREE为3.54~5.72,轻重稀土分馏不明显,其余样品LREE/HREE为9.44~28.74,轻重稀土分馏明显,大离子亲石元素K、Rb、Ba等略显富集,高场强元素Nb相对亏损,与俯冲带玄武岩的微量元素特征较为相似,意味着该类岩石可能与俯冲带构造背景具有一定联系。本次对二叠系树维门科组(P_(1-2^(s)))安山岩进行了LA-ICP-MS锆石U-Pb定年,得到^(206)Pb/^(238)U加权平均年龄值为(297±1.3)Ma,代表该蛇绿岩俯冲的时代可能为早二叠世。结合该蛇绿构造混杂岩物质组成、岩石地球化学特征和锆石U-Pb年代学特征及前人成果研究分析,认为其在石炭纪裂开成洋时期形成,于早二叠世发生俯冲消减,属于SSZ型蛇绿岩。The Kezhitage-Songshishan ophiolitic tectonic mélange,located in the Yinshishan area,Qiemo County,Xinjiang,is subordinate to the part of the western extension of the Muztag ophiolite belt.It is characterized by strongly structural intermixtures,mainly consisting of ophiolite fragments,overlaying rock series,detached blocks,matrix,etc.Among these rocks,the serpentinite and metaperidotite in the ultrabasic complex have SiO_(2) contents varying from 39.40% to 41.51%,high MgO contents(37.97%-38.70%),and low contents of TiO_(2)(0.01%),Al_(2)O_(3)(0.08%-0.72%),and K_(2)O(0.02%-0.03%).In addition,they have Mg^(#)values ranging from 84.36 to 84.90,and m/f values ranging from 10.70 to11.09.Thus they belong to magnesia ultrabasic rock.Their total contents of rare earth elements ∑REE(4.70×10^(-6)-6.09×10^(-6))are slightly higher than those of chondrite.Their(La/Yb)_(N) values vary from 5.80 to 7.72,and their δEu values range from 0.84 to 1.13,indicating that their light rare earth elements(LREE)are relatively enriched.Their contents of Cr,Ni,and Co are relatively high.Especially,their Ni contents have reached the cutoff grade.They also enriched in other elements such as P,Nb,Zr,Hf.The diorite samples within the magmatic rock have relatively low contents of SiO_(2) and K_(2)O,but relatively high contents of MgO,CaO,and Na2O.In the Al_(2)O_(3)-CaO-MgO diagram,they are plotted in the field of mafic cumulates,suggesting that the diorite could also be a part of the ophiolite.The dioritic samples,including quartz diorite and diorite,have LREE/HREE values varying from 3.54 to 5.72,and have no apparent fractionation between LREE and HREE.Other samples(biotite amphibole schist,granitoid,and trachyte)have LREE/HREE values ranging from 9.44 to 28.74,and obvious fractionation between LREE and HREE.Furthermore,they have slightly enriched in large ion lithophile elements(K,Rb,Ba,etc.),relatively depleted in high field strength element Nb,and similar trace element characteristics of the subduction zone basalt,suggesting that this ty

关 键 词：青藏高原 可支塔格—耸石山 蛇绿构造混杂岩 地球化学 俯冲 SSZ型 

分 类 号：P541[天文地球—构造地质学] P599[天文地球—地质学]